This is a simply outstanding example of a '04 Navy shoulder stock.  It has the Crown/M stamp on the wood and on the stock disk.  Apparently, the stock disk was a latter addition to the original stock and on some examples partially removed the Crown/M on the wood.  Two small belt loops have been added one of which has a date of 1918 on it.  The serial number is 758.  All wood and blue finish is original.